CT2 communication systems that utilise available public switched telephone network (PSTN) infrastructure to provide micro cellular wireless communication services are known in the art. A typical CT2 communication system comprises a plurality of portable communication units and a variety of equipment that are coupled to the PSTN. This equipment includes a switching unit and a plurality of telepoint base stations (TBS). Typically CT2 subscribers could initiate calls but could not receive calls, however, recent developments of integrating a paging receiver into the portable communication units, and the use of the switching unit allow calls to be made to, and received by, CT2 subscribers.
With these recent developments, when the PSTN receives an incoming call for a CT2 subscriber unit, the call is routed to the switching unit while the caller is put on hold. The switching unit translates the called number into a pager number and pages the CT2 subscriber, providing the subscriber unit with a selected call back number of the switching unit. Upon receiving the page, the subscriber unit alerts the subscriber who initiates a call to the call back number of the switching unit. Upon receiving the call from the subscriber unit, the switching unit couples the incoming call with the call from the subscriber unit, and direct communication between the caller and the CT2 subscriber unit may then proceed.
Another method of providing CT2 subscribers with the additional capability to receive calls, requires the portable communication units to register with at least one TBS, and the registration information maintained in a central database. With the use a switching unit coupled to the PSTN, when an inbound call for a CT2 subscriber is received, the PSTN forwards the call to the switching unit. Subsequently, an outbound call is made by the switching unit to the CT2 subscriber using the registration information in the central database. When the call to the CT2 subscriber unit is established, the switching unit couples the inbound and outbound calls, thereby allowing direct communication between the calling party and the CT2 subscriber via the switching unit.
The methods described above provide a significant improvement to early CT2 communication systems by allowing CT2 subscriber units to receive calls. However, a significant disadvantage of the paging method is the uncomfortably long period of time a caller is kept on hold while a call to a subscriber unit is established. Yet another disadvantage of the paging method is the need for CT2 subscriber units to be equipped with integrated paging receivers thereby increasing the cost and complexity of the subscriber units. Also, as paging throughput is dependent on user traffic, the paging process can introduce an additional unpredictable delay, further prolonging the time a calling party is kept on hold.
A disadvantage of both methods is the use of an expensive switching unit. The switching unit is coupled to the PSTN using trunk telephone lines, and consequently, is expensive to install, use and maintain. In addition, as the switching unit provides the coupling for each call to a CT2 subscriber, the number of switches i.e. the size of the switching unit, determines the throughput. Hence, to ensure an acceptable grade of service a large switching unit is required.
Therefore, a need exists for a quick and economical method for processing an incoming call in a telepoint communication system that will not require a switching unit to be coupled to the PSTN, preferably does not use paging, and establishes a call from caller to subscriber within a substantially shorter, predictable period of time.